Cover Your Bases for Optimal Almond Pollination

cover crop mix for almond pollination

An almond orchard in Turlock, CA, promotes honey bee pollination with a cover crop grown from the Soil Builder mix made by Project Apis m.
Photo courtesy of Project Apis m.

Good hosts make sure their guests are well fed. In the case of California almond growers, while they bend over backward to invite honey bees to the table, they need to provide a better menu, according to one of the nation’s top honey bee research organizations.

California produces up to 80% of the world’s almonds. Every tree in the crop depends on pollination from honey bees — more than 2 million colonies of them — to pull off what the industry considers to be the “world’s greatest pollination event” each season.

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Although almond pollen itself is full of protein and good for bees, the almond bloom is short. Orchards are not typically places where bees can find good food sources before and after the bloom. This means colonies can struggle to find the proper nutrients that help them thrive.

On top of poor nutrition, honey bees are battling three other P’s — parasites (particularly the Varroa mite), pathogens, and pesticides. Fortunately, there is a common solution to all four problems, which is where Project Apis m., or PAm, intervenes.

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The organization’s anchor forage program, Seeds for Bees, aims to provide growers in California with free or subsidized cover crop seeds. Such forage crops, which include nutritious mustards and clovers, provide food for bees when they need it most. Studies have shown that colonies with access to diverse sources of nutrition have lower pathogen loads and higher overwinter survival rates.

“What’s great is that when that nutrition is there, when it’s ample, it helps mitigate the negative effects of those other issues,” Billy Synk, PAm’s Director of Pollination Programs, says.

“When bee colonies are properly fed, they are communicating about 20% more efficiently than their counterparts that are raised in existing environments where they don’t have access to adequate forage. That communication is how those bees pollinate efficiently.”

Why Forage?

Almond orchards provide the setting for what Synk calls the “positive feedback loop,” in which incoming pollen, increased honey bee brood, and increased foraging are interdependent. This culminates with the first day of almond bloom, typically during the second week of February.

By this time, growers could have planted a bee forage cover crop that blooms before the almonds — by a couple of days, a couple of weeks or, in some cases, Synk says, a full 30 days beforehand.

“If you can start that positive feedback loop, going with nutrition from natural forage — whether it be cover crops, or hedgerows, or natural habitats in the area — by the time the almonds do bloom, those bees … are going to be ready to attack those blossoms,” Synk says. “Your pollination is going to be a lot better for it.”

Seeds for Bees offers four different seed options that act quite differently, Synk says. The ideal option depends on grower goals, concerns, and timing as well as types of soil, irrigation, and equipment.

  • PAm Brassica mix — Comprised of brassicas, including canola, three species of mustard, and daikon radish, “this is going to be the one that, if planted early and irrigated and germinated by Nov. 1 or late October, will bloom before the almonds,” Synk says.
  • PAm Clover mix — Comprised of five different species of clover and medic, the mix is not as good with weed control but very good at nitrogen fixation, Synk says. It is less effective with soil penetration and takes a little more water than the other ones, he adds, but growers who are able to manage a clover mix “really enjoy it.”
  • PAm Soil Builder mix — In just its second year of use, the mix combines brassicas, legumes, and grains. “This has become a very popular mix,” Synk says. “You get a little bit of that early forage, a little bit of that late forage — those legumes are going to be blooming before and after almonds into March and April — and those grains help with biomass and really help choke out the weeds.”
  • Vetch-grain mix — Another legume, vetch blooms later than all the other Seeds for Bees options. Its fine root hairs are excellent at stabilizing the soil surface and preventing erosion. A successful stand can fix more than 100 pounds of nitrogen per acre, Synk says, although vetch should not be broadcasted in young orchards as it may grow up the tree trunks.

Seed Application

Drill seeding is the superior method, Synk says, based on the cost saving that comes with better efficiency and lower plant rates.

“If your soil is very hard, very high clay, chances are most likely that you’ll be able to drill right into that. There are some exceptions,” Synk says. “But that’s another piece of equipment that you have to purchase, store, and maintain.”

Success can be achieved from broadcasting alone, Synk says.

“No seedbed prep is needed. But after you broadcast, you do need to cover up the seed a little bit. The birds will get at it, and when it does rain or you irrigate, it will dry out too quickly if it’s just laying on top of the soil,” Synk says. “These are small seeded, so you only want a quarter of an inch at most deep in there. A piece of chain link fence behind a tractor or four-wheeler, just something to drag a little bit of soil over it, is definitely enough.”

Positive Research

The Almond Board of California (ABC) is funding the “most comprehensive study ever done” on cover crops in orchards, Synk says. “I’m so excited to be involved. We are getting a lot of good preliminary data, and when it’s done will make a great paper.”

Early returns have seen nitrogen improve more than 126 and 82 pounds per acre in Kern and Merced Counties, respectively. Meanwhile, yield has increased 217 pounds per acre in Merced County and 94 pounds per acre in Kern County.

“This was very pleasing to see. I would have been very happy just showing there was no negative yield,” Synk says.

With regard to frost, no air temperature differences were found at 3 feet, and it has been shown that winter ground cover can significantly increase surface soil temperature compared to bare soils in windy situations.

“If there is the potential that the cover crop can decrease temperature and decrease circulation, cover crops are potentially seen as a risk to almonds,” Synk says. “We were really excited to see that there are essentially no temperature differences at 3, 4, or 5 feet and higher. There was a temperature difference at the soil surface, but that’s not really where the nuts are.”

Additional Benefits/Guidelines

First-year enrollees are eligible for a $2,000 discount off their total seed purchase. Second-year enrollees are eligible for a $1,000 discount. All enrollees receive discounted pricing, free shipping, and free technical advice and support.

“Depending on the seed mix you select and the rate that you plant it, $2,000 can be anywhere from between 50 and 120 acres of cover crop seed,” Synk says.

Enrollment each year opens on June 15 at ProjectApism.org/Seeds-For-Bees. Growers must reside in California. They must complete an online application and agree to submit two photos per year along with an annual survey. A short phone consultation with a Seeds for Bees program manager is also required.

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